Which oil for cb750k2

[Pauarc]

Need some help with which oil is best for my k2 mineral or synthetic book tell me mineral but shop are telling me synthetic

[Nurse Julie]

10w40 or 20w50 mineral on a 750 sohc. Synthetic will give you clutch slip.

[McCabe-Thiele (Ted)]

I suspect you could use the  Synthetic technology type - I think they mean semi synthetics!

[Nurse Julie]

No Ted, mineral oil. And if you can get hold of it 20w50 with zinc is the best for a 750K.

[paul G]

10/40W mineral Diesel oil
Been discussed many times 

[McCabe-Thiele (Ted)]

No Ted, mineral oil. And if you can get hold of it 20w50 with zinc is the best for a 750K.

The reality is semi-synthetics perform close to mineral oils - I don't know if the clutch might be an issue as I've not used it. Many sites list semi-synthetics for motor cycles even though they have wet clutches.
https://www.westwayoils.co.uk/products/10w40-semi-synthetic-motorcycle-oil?_pos=5&_sid=c0fba5ec0&_ss=r
The advantage of a semi might be the improved flow properties over just mineral. There is no regulation on the percentage of synthetic oil in the semi type it is my suspicion that the cheaper semis will have a greater mineral content to save money as mineral oil is much cheaper to make. It appears that as modern engine design has moved to fully synthetic so the mineral market has lost its large volume demand so oil companies are just profiteering as mineral oil should be as cheap as chips.

Many brands of Semi oils already contain high levels of zinc, Phosphorous & Sulphur.

https://www.westwayoils.co.uk/products/20w50-classic-oil-high-zinc-semi-synthetic-zddp

Update or https://www.westwayoils.co.uk/products/10w40-semi-synthetic-motorcycle-oil?_pos=5&_sid=c0fba5ec0&_ss=r

[K2-K6]

Technically 20w50 is too thick viscosity for the specification needed.

It will, unless always heated to correct range, mean reduced flow volume through any of the flow restrictions in these engine.

Ultimately they are a true 30 viscosity design.

Running 20w50 at below realistic hot temperatures will result in the oil pump output being dumped through its pressure release valve as too much pressure accumulation in system distribution, resulting in stalling volumes throughout the engine under these circumstances.

[royhall]

I tried Mineral 20W50 in my CB750F2 and it appeared to have no negative effect on the engine, but it did make the rattly clutch somewhat quieter. This is the oil I used   Millers Oils Classic 4T 20w-50 Mineral Motorcycle Engine Oil - 4 Litres 5024081844747 | eBay

[davidcumbria]

10w40 or 20w50 mineral on a 750 sohc. Synthetic will give you clutch slip.

Is that also the same for a 550 k1?

[Bryanj]

Yep, 10w40 or 15w40. 20w50 is a bit thick for UK normal temps but ok for 40 deg summers

[Pauarc]

I have now put new 10w40 oil in and changed the filter so hopefully it will help with dragging clutch I did have 20w50 in I will try again

[sprinta]

Have been using 10/40W semi synthetic in both my 73 750K2 and 76  Z900A4 for several years and have had no problems with the clutch on either bike.

[McCabe-Thiele (Ted)]

I now have semi-synthetic in my 400 - no clutch slip either - modern oils do have lots of benefits IHTBS.

We used to run a R3mR Terrano - all the purists said you had to use mineral oil - I found it ran much quieter on semi or fully synthetic. My late mothers slab sided Micra would weep oil from the front seal for the first few days - then it would magically go as the additives worked their magic. (covered over 100k miles)

Aside from the potential  clutch slip issue (hence why I would stick with semi-S) modern oils have additives that help keep seals supple, reduce sludge/tar build ups inside the engine casings, maintain the right viscosity, have added micronised chalk to neutralise acid build up plus they get everywhere they need to. Yes they can be quite searching - hence why they can reduce engine noise.

[Moorey]

 
 As has been discussed many many times before Mineral diesel oil. Preferably with a good zinc content.

[McCabe-Thiele (Ted)]

The Diesel option is interesting a major component of diesel oils is the detergent content that holds the carbon particles in suspension. If you change the oil in a diesel engine it's nice clean oil - within a short space of time the oil turns  black.

Having never used diesel engine oil in a petrol car it would be interesting to know how long it keeps looking clean for.

Modern petrol engines now manufactured with fine tolerances plus lean burn technology do seem to keep the oil clean looking for much longer.